This invention relates to a nondestructive examining apparatus.
With recent industrial development, high performance and high reliability are required by various machines and apparatus. For example, nuclear reactor containers are subjected to nondestructive examination not only during manufacturing but also during operation thereof. During the operation of a nuclear power plant due to the danger of radioactive radiation and during the machining of such narrow elements as nozzles, it is difficult for the operator to approach them. Moreover, from the standpoint of efficiency and safety, remote control and automation of the examining apparatus are highly desirable.
In pumping up stations too, due to the increase in the capacity of individual machines and the sites of installing the stations, demand for pump-turbines capable of operating under high heads is increasing. The configuration of the water flow path of a water wheel becomes extremely complicated for the purpose of minimizing the resistance of the flow path and maximizing the efficiency of the water wheel. Since the same water wheel is operated as either a pump or a turbine the cross-section of the flow path is becoming more complicated and narrow. Accordingly, development of a novel method and apparatus capable of accurately examining such complicated narrow portions without destroying them has been desired.
FIG. 1 shows a longitudinal cross-section of one example of the runner of a pump-turbine which rotates about a center shaft 1 and includes a plurality of water flow paths A, and FIG. 2 shows a cross-sectional view taken along a line II--II in FIG. 1. The nunner is made up of a shroud ring 2 and a crown plate 3 between which are provided a plurality of vanes 4.sub.a through 4.sub.f. The flow paths defined by these vanes 4, the crown plate 3 and the shroud ring 2 are generally narrow and long and each vane extends spirally about one half about the periphery of the center shaft 1.
FIGS. 3a, 3b and 3c show cross-sectional views of the flow paths of the runner in which FIG. 3a shows a flow path 5.sub.a near the shaft 1, FIG. 3b that of 5b at an intermediate portion, and FIG. 3c that of 5.sub.c near the outer periphery of the runner. In a case of a pump-turbine having a capacity of 200-300 MVA, and operating under a head of 500-600 meters, the width of the flow paths changes from about 150 mm at 5.sub.a to about 500 mm at 5.sub.c, while the height of the path varies from about 600 mm at 5.sub.a to about 200 mm at 5.sub.c. Also the angle of each flow path varies continuously, and the length thereof amounts to about 4 m. Especially, in a hydroelectric power station, guide vanes and stationary vanes are disposed about the runner so that it is difficult to access the runner.
As the head and capacity of the pumping up station increase, the mechanical strength of the runner and the construction of the flow paths should be more vigorously controlled so that during manufacturing it is necessary to detect defects of the material and welds, and during running, at a definite interval, it is essential to detect or examine cracks caused by stresses, surface damage due to cavitation, and damage caused by gravel and sand contained in the water. In a prior art plant having a small capacity and operating under a low head, the operator can enter into the flow paths to perform such nondestructive examinations as penetration defect location and magnetic powder fault detection. However, in a large plant operating under a head of 500 to 60 meters, or 1000 meters, the operator cannot enter into the flow paths. Even if the operator can enter into the flow paths he must work under dangerous conditions so that development of a new type of nondestructive examining apparatus has been desired.